cp's OEIS Frontend

A056252 Indices of primes in sequence defined by A(0) = 33, A(n) = 10*A(n-1) - 7 for n > 0.

%I A056252 #20 Jan 17 2019 13:44:05
%S A056252 5,7,893,1523,3035,21155
%N A056252 Indices of primes in sequence defined by A(0) = 33, A(n) = 10*A(n-1) - 7 for n > 0.
%C A056252 Numbers n such that (290*10^n + 7)/9 is prime.
%C A056252 Numbers n such that the digit 3 followed by n >= 0 occurrences of the digit 2 followed by the digit 3 is prime.
%C A056252 Numbers corresponding to terms <= 3035 are certified primes.
%D A056252 Klaus Brockhaus and Walter Oberschelp, Zahlenfolgen mit homogenem Ziffernkern, MNU 59/8 (2006), pp. 462-467.
%H A056252 Patrick De Geest, <a href="http://www.worldofnumbers.com/deplat.htm#pdp323">PDP Reference Table - 323</a>.
%H A056252 Makoto Kamada, <a href="https://stdkmd.net/nrr/3/32223.htm#prime">Prime numbers of the form 322...223</a>.
%H A056252 <a href="/index/Pri#Pri_rep">Index entries for primes involving repunits</a>.
%F A056252 a(n) = A082705(n) - 2.
%e A056252 3222223 is prime, hence 5 is a term.
%t A056252 Select[Range[0, 2000], PrimeQ[(290 10^# + 7) / 9] &] (* _Vincenzo Librandi_, Nov 03 2014 *)
%o A056252 (PARI) a=33;for(n=0,1600,if(isprime(a),print1(n,","));a=10*a-7)
%o A056252 (PARI) for(n=0,1600,if(isprime((290*10^n+7)/9),print1(n,",")))
%Y A056252 Cf. A000533, A002275, A082705.
%K A056252 nonn,hard,more
%O A056252 1,1
%A A056252 _Robert G. Wilson v_, Aug 18 2000
%E A056252 Additional comments from _Klaus Brockhaus_ and Walter Oberschelp (oberschelp(AT)informatik.rwth-aachen.de), Dec 20 2004
%E A056252 Edited by _N. J. A. Sloane_, Apr 17 2007
%E A056252 More terms from Herman Jamke (hermanjamke(AT)fastmail.fm), Jan 02 2008
%E A056252 Comments section updated and a link added by _Patrick De Geest_, Nov 02 2014
%E A056252 Edited by _Ray Chandler_, Nov 05 2014